From Förberedande kurs i matematik 1

To get \displaystyle x by itself on the left-hand side, we subtract \displaystyle 1 from both sides

\displaystyle 2x+1-1=13-1

which gives

\displaystyle 2x=12

Then divide both sides by 2,

\displaystyle \frac{2x}{2}=\frac{12}{2}

to get \displaystyle x:

\displaystyle x=6